1. Field of the Invention
The present invention relates to a base station of a mobile communication network, and more particularly to a transmission power control apparatus of a base station of a mobile communication network.
2. Description of the Background Art
Generally, an up-converter of a transmitter in a base station of a mobile communication network converts an intermediate frequency (IF) signal to a radio frequency (RF) signal and controls the RF signal to have a suitable level of power (strength). For this purpose, the transmitter includes a voltage detecting unit, an automatic gain controller and an attenuator to detect the strength of a signal on the transmission path and generates a control signal to control the gain of the signal.
And, a different voltage detecting unit and a different controller constructed in other circuit board detect the strength of the signal outputted from the up-converter and control the gain of the signal to have the appropriate strength.
FIG. 1 is a schematic block diagram of the transmitter of a base station of a mobile communication network in accordance with a conventional art.
As shown in the drawing, a transmitting apparatus of the mobile communication network in accordance with the conventional art includes an up-converter 101 for converting a received intermediate frequency (IF) signal to an RF signal and controls the gain of the converted RF signal, a high power amplifier (HPA) 14 for amplifying the RF signal outputted from the up-converter 101 to a high power, a coupling unit 102 for receiving the high power RF signal from the HPA 14, extracting only a required specific frequency band component of the RF signal, and outputting the extracted signal to an antenna and to a voltage detecting unit 103, the voltage detecting unit 103 for converting the RF signal received from the coupling unit 102 to an IF signal and detecting a voltage level in proportion to the strength of the converted IF signal, and a controlling unit 104 for receiving the detected voltage and outputting a Tx_RF_GAIN signal.
The voltage detecting unit 103 and the controlling unit 104 serve to judge whether the RF signal on the transmission path has the proper strength and monitor it.
The up-converter 101 includes a splitter 2 for splitting an inputted signal to two different paths, fixed attenuators 3 and 21 for attenuating the power (strength) of the received signal; amplifiers 4 and 11 for compensating a loss generated during the process of attenuating a power, SAW filters 5 and 20 for extracting a required signal among signals outputted from the amplifier 4, a frequency up mixer 8 for converting the IF signal to an RF signal, a local oscillator 6 for generating a single frequency signal and providing it to the frequency up mixer 8, band pass filters (BPF) 7 and 9 for passing only a specific band signal, a voltage variable attenuator 10 for attenuating the power (strength) of the received signal under the control of the automatic gain controller 27, a coupler 12 for coupling a received signal to two elements, an isolator 13 for removing a reflection wave causing a transmission distortion, voltage detectors 26 and 28 for detecting a voltage level in proportion to the strength of the inputted signal, and the automatic gain controller 27 for generating a gain control signal for controlling the voltage variable attenuator 10.
The operation of the transmitter of the mobile communication network base station in accordance with the conventional art constructed as described above will now be explained.
An IF signal 1 inputted to the up-converter 101 is split to two paths by the splitter 2, and while the IF signal passes the first fixed attenuator 3, the amplifier 4 and the first SAW filter 5, a noise is canceled to a degree. And then, the IF signal is converted to an RF signal by the frequency up mixer 8 and the first local oscillator 6 and outputted to the second band pass filter 9.
As the RF signal passes the second band pass filter 9, its specific frequency band component is extracted, and the gain of the filtered signal is controlled to be down by the voltage variable attenuator 10 and outputted to the amplifier 11.
The amplifier 11 amplifies the power-attenuated RF signal to a certain level and outputs it to the isolator 13, and the isolator 13 removes the reflection wave included in the RF signal to prevent generation of a transmission distortion. The reflection wave-removed RF signal is outputted to the HPA 14.
The RF signal is amplified by the HPA 14 to have a high power and outputted to the coupling unit 102, so that an unnecessary frequency component of the RF signal is removed by the front end filter 15 of the coupling unit 102 and outputted back to the antenna, and also coupled by a directional coupler 16 of the coupling unit 102 so as to be outputted to the voltage detecting unit 103.
In the voltage detecting unit 103, the RF signal is converted to the IF signal by the second oscillator 18 and the frequency down mixer 17 and outputted to the amplifier 19. The second local oscillator 18 generates a signal having a single frequency and provides it to the frequency down mixer 17.
The IF signal is amplified by the amplifier 19 and inputted through the second SAW filter 20 and the second fixed attenuator 21 to the second voltage detector 22. The second voltage detector 22 detects the voltage of the received IF signal and outputs it to the controlling unit 104.
In the controlling unit 104, the voltage level signal (an analog signal) is converted into a digital signal and inputted to the controller 24. The controller 24 judges whether the RF signal transmitted through the antenna has a proper strength, computes a difference value (xcex94) between the voltage detected by the voltage detecting unit 103 and a reference voltage and provides a Tx_RF_GAIN signal corresponding to the difference value (xcex94) to the automatic gain controller 27. The controller 24 holds a Tx_RF_GAIN signal table corresponding to each voltage difference value.
In the up converter 101, the coupler 12 positioned before the isolator 13 outputs the received RF signal to the first voltage detector 26. The first voltage detector 26 detects the voltage level of the received RF signal and outputs it to the automatic gain controller 27. And, the third voltage detector 28 also receives the IF signal split by the splitter 2, detects the voltage level of the IF signal and outputs it to the automatic gain controller 27.
Consequently, the automatic gain controller 27 generates the gain control signal by using the voltage inputted from the first voltage detector 26, the voltage inputted from the third voltage detector 28 and the Tx_RF_GAIN signal inputted from the controlling unit 104, and controls the whole outputting of the transmitting apparatus by providing the generated gain control signal to the voltage variable attenuator 10.
That is, the automatic gain controller 27 generates the gain control signal according to the strength of the RF signal provided from the first voltage detector 26, or generates the gain control signal according to the Tx_RF_GAIN signal provided from the controlling unit 104, to control the strength of the RF signal transmitted through the transmission antenna.
The conventional transmission power controlling apparatus of the mobile communication network base station, however, has the following problems.
That is, since the voltage detector, the filter, the local oscillator and the frequency mixer are used redundantly, the production cost of the system is increased.
In addition, the path loss and the deviation due to the allowable error of the elements occurring in the circuit itself which monitors and controls the output signal.
Moreover, the gain control signal may be varied depending on what value a system sets as an initial value when the up-converter is manufactured, and when the base station transmitter is installed, since the calibration is made for the power (strength) of a signal transmitted to the antenna, it is difficult to verify whether the up-converter operates properly without any trouble.
Therefore, an object of the present invention is to provide a transmission power control apparatus of a base station of a mobile communication network which does not include any redundant parts, and in which a signal gain of an up-converter can be also adjusted by an external source.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a transmission power control apparatus of a base station of a mobile communication network including: an up-converter for converting a received intermediate frequency (IF) signal to a radio frequency (RF) signal and outputting it; a high power amplifier for amplifying the power of the signal outputted from the up-converter; a coupling unit for receiving the signal from the high power amplifier, extracting only a signal of a necessary frequency band and outputting the extracted signal to an antenna; an attenuator for receiving the signal from the coupling unit, controlling the gain of the signal and outputting it to the up-converter; a comparing unit for comparing the gain control signal applied from the up-converter and the gain control signal inputted from an external source and controlling the attenuator; a controlling unit for providing the gain control signal inputted from the external source to the comparing unit; and an automatic gain controller for generating a gain control signal, control a signal gain of the up-converter and providing the gain control signal to the comparing unit.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.